Wood anatomy of conifers from the upper triassic and lower jurassic strata oh the argentina

GNAEDINGER SILVIA; KLOSTER ADRIANA; CRISAFULLI, A; ZAVATTIERI, A. M.; GOMÉZ, NOEMÍ

Conferencia; IAWA Pan American meeting; 2012

Conifer woods from Upper Triassic and Lower Jurassic beds of Argentina are described. The morphogenera Agathoxylon Hartig, Podocarpoxylon Gothan and Protophyllocladoxylon Kräusel occur in the Upper Triassic Llantenes Formation (Mendoza province) and Laguna Colorada Formation (Santa Cruz province), while the morphogenera, Kaokoxylon Kräusel, Agathoxylon Hartig, Podocarpoxylon Gothan, Brachyoxylon Hollick and Protojuniperoxylon Eckhold occur in the Lower Jurassic El Freno Formation (Mendoza province), Piedra Pintada Formation (Neuquén province) and Roca Blanca Formation (Santa Cruz province). Kaokoxylon Kräusel has characteristic features of pith, primary endarch and secondary xylem. Both Agathoxylon and Kaokoxylon have araucarian type xylem (contiguous and alternate pitting). Brachyoxylon, Circoporoxylon, Protophyllocladoxylon and Protojuniperoxylon have mixed type secondary xylem (araucarioid, mixed and abietinoid pitting) but differ in cross-field pitting type, having araucarioid type, circopore type (oopores and circular pits), phyllocladoid type (simple, large pits) and, cupressoid pits, respectively. Protojuniperoxylon has thick ray parenchyma walls with nodules and obvious pits. Podocarpoxylon is of abietinean type (radial pitting, separate and opposite) and has podocarpoid cross-fields. The diversity of conifer wood shows that during the Triassic-Jurassic there were three types of woods: araucarian-type considering as a legacy from the Paleozoic conifers, and characteristic of the current Araucariaceae; the abietinean type is encountered in most extant species of the conifers. The third type of mixed secondary xylem is more particular to those Jurassic - Lower Cretaceous wood conifers (but not exclusive). Most of the Mesozoic species identified as Agathoxylon and Kaokoxylon are related to the Family Araucariaceae. The genera identified as Podocarpoxylon, Circoporoxylon and Protophyllocladoxylon show affinity to the Podocarpaceae. The genus Protojuniperoxylon is related to Cupressaceae and the Jurassic-Cretaceous Brachyoxylon included in the extinct family Cheirolepidiaceae.